1. Field of the Invention
The present invention relates generally to a wireless charging network, and more particularly, to wireless power transmitter and receivers, and a method for permitting, by a wireless power transmitter, a wireless power receiver for charging in a wireless charging network.
2. Description of the Related Art
Mobile terminals, such as cell phones, Personal Digital Assistants (PDAs), etc., are powered by rechargeable batteries, and often use separate charging devices to recharge these batteries.
Typically, a charging device and a battery, each having contacting terminals on an outer surface thereof, are electrically connected by connecting their contacting terminals to each other. However, when using a contact charging method, the contacting terminals are often contaminated with dirt or rust, leading to inappropriate battery charging.
To address this problem, wireless charging or contactless charging technologies have been developed and applied to many different electronic devices. For example, using wireless charging, a battery of a cell phone is automatically charged by placing the cell phone on a charging pad, without using a separate charging connector.
Examples of wireless charging technology include an electromagnetic induction method using coils, a resonance method using resonance, and a Radio Frequency (RF)/microwave radiation method that converts electrical energy into microwaves for transmission.
The method based on electromagnetic induction transfers power between primary and secondary coils. More specifically, moving a magnet around a coil produces an induced current, based on which a magnetic field is produced at a transmission end. The change in the magnetic field at a receiving end induces a current to generate energy. This phenomenon is commonly referred to as “magnetic induction,” and the wireless power transmission method based on the magnetic induction provides superior energy transmission efficiency.
In the resonance method using resonance, resonant electrical energy of electromagnetic waves is directly transferred only to a device having a same resonant frequency, and a non-used part of the energy is re-absorbed into the magnetic field, rather than being dispersed in the air. Consequently, the resonant electrical energy is not deemed harmful to surrounding machines or bodies.
Although studies on the various wireless charging methods have recently been done, standards for prioritizing wireless charging, searching for wireless power transmitters/receivers, selecting the communication frequency between the wireless power transmitter and receiver, adjusting the wireless power, selecting a matching circuit, distributing communication time for each wireless power receiver in a single charging cycle, etc., have not yet been suggested.